Albert Einstein
told us that a star or other massive object distorts spacetime in its
vicinity. Sufficient distortion makes it impossible to describe matter
and motion with the single "inertial reference frame" used
in Newton's theory of mechanics and Einstein's theory of special relativity.
General relativity describes the distortion of spacetime near a star,
white dwarf, neutron star, or black hole and predicts the resulting
motion of stones, satellites, and light flashes.

Learning general relativity usually requires mastering Einstein's field
equations, which are expressed in the complicated mathematics of tensors
or differential forms. But big chunks of general relativity require only
calculus if one starts with the metric describing spacetime around Earth
or black hole. Expressions for energy and angular momentum follow, along
with predictions for the motions of particles and light. Students study
the Global Positioning system, precession of Mercury's orbit, gravitational
red shift, orbits of light and deflection of light by Sun, frame-dragging
and precession near a rotating body, gravitational waves, and two different
models of the Universe.